From The Giant: The Definitive Obey Giant Site
In 1994, Coca-Cola released "OK Soda," a soda attempting to infiltrate "Generation X" by using a grass-roots/street campaign. Attempting to cash in on Shepard Fairey's Obey Giant campaign, OK Soda used a very similar look with its logo and images. To spark interest, Coca-Cola passed out stickers and put up posters before the soda ever hit stores. As retaliation, Shepard took one of their illustrations and changed it from "OK" to "AG" (for André the Giant). Shepard started putting up stickers and posters simultaneously (AG Soda and AG Soda Variant). Some people were confused as to which one came first, and when Shepard was putting up knockoff posters in Boston, some passers-by yelled, "Hey, all right -- OK SODA!!!"
An obvious note: the soda did not survive, and was discontinued in 1995.
From Supply and Demand, pg. 29:
In 1994, the Coca-Cola Company came out with OK Soda, designed to look like an underground, upstart soda brand. They chose Daniel Clowes and Charles Burns, underground comic book artists, to design graphics for three different cans. I didn't know anything about OK Soda, but one day while I was visiting my parents, my dad said, "Hey, Shep, I saw this article in Time and left it on your bed. It looks kinda like the stuff you're doing. Maybe you should contact this company and do some work for 'em." The article was about this new soda that was riding the "grunge" wave. I was really insulted by OK Soda because it was manipulative: they didn't want people to realize it was Coke. I felt like it was intruding on underground culture, trying to exploit it. I thought there was going to be a national campaign, but it was actually just test-marketed in nine cities, and by coincidence, one of them was Providence and another was Boston. l decided I would make a mockery campaign to sabotage what they were doing, and since the graphics were in Time but the product wasn't out, I figured I could beat them to the punch and totally confuse people. Instead of "OK" I used "AG" and changed the copy from "the more OK you consume, the more OK you feel" to "the more AG you consume, the more AG you feel." l measured the placards in the subway in Boston and made my posters to fit in over the real OK Soda ads. One time when I was out postering in Providence, some guys drove by and asked me what I was putting up. I held up my poster, and they shouted, "OK Soda!" It only confirmed my suspicion that people don't pay very close attention to anything.